This invention relates to an apparatus and a method for filtering biological samples. More specifically, an apparatus and a method can be provided for the filtration of biological samples via gravitational filtration techniques.
One field of gravitational filtration is the separation of parasites and parasite eggs from fecal samples. In the past, this area of technology has relied upon a variety of filtration techniques and filtration apparatus. These separation procedures have typically been categorized as either closed or open.
An open filtration procedure relates to one in which sample is poured from a specimen collection container into a apparatus containing a filter of some type, usually gauze or an integral screen, in order to separate solid particulate matter from the liquid. The separated liquid typically includes parasitic objects including eggs and larva. This filtering apparatus is placed on top of a desired container which collects the filtered liquid portion of the fecal sample.
The term closed filter procedure refers one which utilizes a filtering apparatus designed to interconnect both the sample collection container and the intended receiving container for the filtered liquid portion of the sample. Using this sort of apparatus one can interconnect the sample collection and the transport container to the intended container so that they are in communication with each other. Then, one can allow gravity or centrifugation to accomplish filtration rather than by active sample pouring.
Closed procedures allow those performing fecal parasite separation and concentration procedures to avoid the potential for spilling and contamination which are inherent in open procedures. They also minimize the odor associated with processing fecal specimens. The prior art closed techniques have however suffered from several shortcomings. The filter units of closed fecal filtration apparatus tend to become clogged or blocked with particulate fecal matter. This clogging creates a pressure imbalance characterized by the inability of gas to pass between the destination container and the sample container. The inability to equalize gas pressure prevents liquid from flowing into the destination container and halts the filtration process. Additionally closed filtration apparatus typically have a flat filter section with a small surface area compared to the volume of the introduced fecal sample. This proportionally small surface area ratio slows the sample filtration and can even restrict flow entirely.
None of the prior art solutions has been completely effective at overcoming the habit of clogging with particulate fecal matter and none has addressed the inadequate surface area provided by a flat filter that is limited in area by the restrictions imposed by the diameter of the commercially available centrifuge tubes used as containers.
U.S. Pat. No. 4,081,356 discloses a filter apparatus for closed filtration of a fecal sample with a threaded attachment to a commercially available centrifuge tube, a flat circular filter, a central but non-integral tube for gas flow, and a cylindrical friction attachment point for a commercially available standard patient specimen transport container. In this technology the small non-integral gas exchange tube can easily become occluded or pushed into the container tube causing pressure imbalance and interruption of filtration. The filter of this technology is a flat disc with the approximate diameter of a commercially available centrifuge tube.
U.S. Pat. No. 4,675,110 discloses a filter apparatus for closed filtration of a fecal sample with a threaded attachment to commercially available centrifuge tube, a flat circular filter, and peripheral gas exchange channels arrayed in a circular pattern along a bordering lip which is positioned perpendicular to the downward flow of the patient sample. The gas exchange channels in this apparatus are by necessity small to prevent passing particulate fecal matter but are resultantly prone to clogging. The filter is a flat disc with the approximate diameter of a commercially available centrifuge tube.
U.S. Pat. No. 5,556,544 discloses a filter apparatus for closed filtration of a fecal sample with a threaded attachment to a commercially available centrifuge tube, a flat circular filter, a central but integral stem for air gas flow, and a cylindrical friction attachment point for a commercially available standard patient specimen transport container. The air exchange stem in this technology is integral to the filter apparatus but still below the potential level of the liquid created by the addition of the sample to the filtration apparatus and still therefore subject to clogging. The filter of this technology is a flat disc with the approximate diameter of a commercially centrifuge tube. U.S. Pat. No. 5,925,250 is similar to U.S. Pat. No. 5,556,544 except for an outward sheath which prevents cross contamination.
U.S. Pat. No. 5,624,554 discloses a filter apparatus which is integral to and provided with the cap of a patient sample collection and transport container. This apparatus integrates specimen collection and filtration but relies on positive pressure to force specimen filtration. Therefore, this apparatus is subject to potential clogging, leaking, and spraying.
U.S. Pat. No. 6,296,763 discloses a system for closed filtration which encompasses a unique specimen collection tube, filtration apparatus, and container tube. The filtration method in the preferred embodiment of this system is via centrifugation and therefore requires special equipment.